Switching system



March 2,1937. T. A. SPENCER swflcnme SYSTEM Filed Aug. 13, 1935 8 Sheets-Sheet l I I 2 I Z 2 -7.'A. BY v ATTORNE FIG.) v FIG. 2 FIG. 3

March 2, 1937. T, A. SPENCER 2,072,434

SWITCHING SYSTEM Filed Aug. 13, 1935 8 Sheets-Sheet 2 7.34 NCER ATTORNE March 2, 1937. T. A. SPENCER 2,072,434

-swx'rcnmc SYSTEM I Filed Aug. 13,1935 8 Sheets-Shet :s

//v 71A. N ER 81 Arron/air March 2, 1937.

FIG. 4

8 Sheets-Sheet 4 By avg 2m ATTORNEY March 2, 1937. -fl 2,072,434

SWITCHING SYSTEM Filed Aug. 15 1935 8 Sheets-Sheet 5 FIG. 5 v 506 ATTORNEY March 2, 1937. 1'. A. SPENCER SWITCHING SYSTEM Filed Aug. 13, 1935 8 Sheets-Sheet 6 INVENTOR TASPENCER BY FIG. 6

March 2, 1937., T, A SPENCER 2,072,434

swmcame sysmn Filed Aug. '13, 14935 a Sheets-Sjz'et 7 ma FIG. 7

LINES 26 T050 LINES 5/ T0 75 LINES 75 722/00 -4 10 72mm lNl/EN TOR ZASPENCER ATTORNEY March 2, 1937. T. A. SPENCER SWITCHING SYSTEM Filed Aug. 13, 1935 8 Sheets-Sheet 8 8 l. M 5 6 1051210 "10ml 91 B10 710 61 "W 0 1 a c W1 1 q "l -4 51 //v VENTOR TASPENCER ATTORNEY igg la w e o M e "1 81 3 0x10 al 51 4 61 9 3 4 71.01 4 1.0 n u a 1 LINES Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE SWITCHING SYSTEM Application August 13, 1935, Serial No. 35,926

9 Claims.

This invention relates to switching mechanism and particularly to a switching mechanism of the type used in automatic telephone systems.

The object of the invention is to increase the accessibility of the lines of a group by increasing the number of appearances of each line in the switching mechanism, while at the same time preserving a high degree of efficiency in the service given said lines.

A feature of the present invention is an arrangement of lines in a switching mechanism in which the lines are divided in groups of different sizes and assigned tocoordinate rows of contacts in said mechanism, each group appearing in rows of contacts in both coordinate directions.

Another feature is .an arrangement of lines in a switch mechanism comprising a plurality of cross-bar switches in which the lines are divided into groups of different sizes and assigned to the m) contacts of said switches in such a way that each group appears in vertical rows of contacts in some of said switches and in horizontal rows in other of said switches.

Another feature of the invention is a switch in which each line occurs in one group comprising a given combination of lines, which group appears both in a horizontal row and in a vertical row, and also occurs in a second group comprising a different combination of lines, which second group likewise appears in a horizontal and in a vertical row.

These and other features will be described more in detail in the following description and will also be set forth in the appended claims.

5 In the accompanying drawings, Figs. 1 to 6, inclusive, when placed together as indicated in Fig. 9, show complete circuit connections for a line switch arrangement in cross-bar systems in which subscriber stations may be connected with 6 idle trunk circuits leading to selector switches (not shown). Figs. 7 and 8 are schematic illustrations showing how the lines of a group may be assigned to the contacts of a switch mechanism.

.45 The cross-bar switches shown in Figs. 3, 6, '7 and 8 may be or any well-known type, such as the one described in detail in the pending application of J N. Reynolds, Serial No. 702,453, filed December 15, 1933, granted as Patent 2,021,329

50 Nov. 19, 1935. While the invention is described in connection with switches of the cross-bar type, it may be practiced in its broader aspects with other kinds of switches. It will also beobvious from further description that the features of this invention need not be confined to a line switch arrangement of the kind to be described, but may equally well be applied to other switching stages and to trunking systems generally, wherein it is desired to concentrate trafiic on a reduced number of trunks or to automatic tele- 5 phone systems wherein the subscriber lines are made accessible to a smaller number of switching mechanisms.

For the purpose of simplifying this description,

only one switch contact is shown at each cross- 10 point in the sleeve or control lead for each line, whereas the switch in actual practice would carry three or more contacts at each cross-point, two contacts being required for the talking leads and one for the sleeve lead shown at the top of 15 Figs. 1 and 2. The arrangement of the switches is such that any contact set is capable of operation upon conjoint displacement in definite order of two bars, illustrated in Figs. '7 and 8, which intersect in the locality of this set of contacts. The contact sets are maintained actuated by the displacement of the last actuated one of the two bars, and are restored to normal on the release of the last actuating bar. The first bar to be actuated in operating any given contact set is referred to as the horizontal bar and is actuated by a selecting magnet shown immediately to the left of each row of contact sets in each switch, and the second bar to be actuated is referred to as the vertical bar, actuated by a holding magnet shown directly below the vertical row of contact sets in each switch unit.

The schematic of the line switch arrangement above referred to is shown in Fig. 7 in order to illustrate in a general way the manner in which subscriber lines are given access to outgoing trunk circuits. Cross-bar switch LBI is the same as shown in detail in Fig. 3 and provides for twenty-five subscriber lines wherein each line has four multiple appearances arranged so that each may have access to any one of four trunks out of a total of ten trunks. To accomplish this feature, a definite order of multipling is employed as will be evident by referring to the dotted lines 10!, N2, 103 and "H14 which have been drawn to indicate where one set of multiple stops and another begins. Between the lines HH and H12, for example, as will be hereafter described, each of the twenty-five lines has one appearance and a call from any of these lines 5 will be completed through this multiple appearance as long as the trunk available to the line callingis idle. If said trunk is busy, then the call will be completed through a second appearance of the line. This second appearance is shown by the enclosure within the dotted lines I02 and I03. When the trunk available to the calling line in this multiple appearance is likewise busy, then the call will be completed through a third multiple appearance as indicated by the enclosure between the dotted lines I03 and 104. If the trunk available to the line that is calling is also busy, then the call will be completed through a fourth multiple appearance as limited by the dotted lines I04 and MI. Line I, for example, represented by lead I03, would first beconnected over lead 3| I and corresponding cross-bar switch contact I to trunk 305, but if the latter trunk is busy, line I will be connected over leads I03 and 3I2 to trunk 30I. If both trunks 305 and SM are busy, the calling line I will be connected over leads I03 and 3I3 to trunk 3I0. If trunks 305, 30I and 3I0 are busy, the line will be connected over leads I03 and 3I4 to trunk 306. In this manner, the twenty-five lines are arranged so that each has an equal number of trunk accesses which are definitely grouped and numbered as shown.

The number of calls originating on twenty-five subscriber lines as a general thing would not be sufficient to keep ten trunks busy. This invention,.therefore, contemplates the desirability of connecting the same trunks to contact points of other cross-bar switch banks shown in Figs. 6 and '7 within the rectangles LB-2, LB3 and LB-4. It will be obvious from this arrangement that a greater or lesser number of banks may be given access to a given group of ten trunks sufiicient to keep them busy. It will also be evident that the associated circuits must be so arranged that a calling line will be directed in a definite order, one at a time, toward the first of the four choices of trunks that are idle. While for descriptive purposes, four groups of twenty-five lines are assumed together with their associated circuits as shown in Figs. 1 to 6, it will be obvious that any number of groups of lines could be provided for by a simple modification or extension of the circuits shown.

In the system of this invention, every line, in general, has access to four different trunk circuits and to avoid interference a definite sequence of access is provided for each line. It is, therefore, necessary to first know or identify the calling line. To do this, a line and cut-off relay is provided for each line as shown in Figs. 1 and 2, said relays being mounted in ten vertical rows of ten line relays L and then cut-01f relays CO per row. The drawings, for example, show line and cut-off relays connected to identifying leads I04 and I05 for lines I, 5, 6 and I in the first row; line and cut-01f relays connected to leads I06 and I0I for lines II, I5, I6 and 20in the second row; line and cut-off relays connected to leads I00 and I09 for lines 2I to 25 in the top half of the third row. These relays provide for the first group of twenty-five lines appearing in cross-bar switch bank LB-I shown in full in Figs. 3 and 7. Since the sequence of line appearances in the other three groups of twenty-five lines is identical with that of the bank LB-I, only enough line and cut-ofi relays in Figs. 1 and 2 are shown to illustrate the three additional groups of lines. Line and cut-off relays for line 26 thus represent a fourth row of ten sets of relays connected to identifying leads 0 and. III for lines 26 to 35; no relays are shown in the next or fifth row for lines 36 to 45 except identifying leads II2; line and cut-off relays for line 50 represent a row of relays connected to mam leads [I3 and H4 for lines 46 to 50 and would be mounted in the bottom half of the third row with relays for lines 2I to 25. These relays, therefore, represent the line and cut-off relays for the second group of twenty-five lines appearing in cross-bar switch bank LB-2 of Fig. 6. For the third group of twenty-five lines, line and cut-off relay 5I of Fig. 2 represents the sixth row of ten sets of relays connected to identifying leads 20I for lines 5I to 60; no relays are shown in the next or seventh row for lines 6| to I0 but identifying leads 202 are shown; line and cut-off relay I5 represents the top half of the eighth row connected to leads 203 for lines II to I5. In like manner for the fourth group of twenty-five lines appearing in line bank LB--4 of Fig. 6, the line and cut-off relay I6 of Fig. 2 represents a. ninth row of ten sets of relays connected to identifying leads 204 for lines 16 to 85; no relays are shown in the next or tenth row for leads 85 to 96 but identifying leads 205 are shown; line and cut-off relay I00 represents the bottom half of the eighth row connected to identifying leads 206 and 201 for lines 96 to I00.

A calling line is identified by the location of its line and cut-off relays in a given horizontal and a given verticalrow of the L and CO relays just described. The A and B relays of Fig. 2, located opposite each of the ten horizontal rows of L and CO relays, are used to determine the horizontal row, while the C relays at the top of Figs. 4 and 5 are used to determine the particu:.

lar vertical row in which the calling line is 19-.,

cated. These relays, in conjunction with relays 50I to 505 of Fig. 5, also serve to prevent more than one line at a time from being assigned an idle trunk by virtue of the fact that only one set of A and B relays and one set of C relays remains operated during the assignment of a trunk to an incoming call. Trunk busy relays TKI to TK-I0 are provided as shown in Figs. 4 and 5, one for each outgoing trunk so that if the trunk is busy the circuits to the selecting and holding magnets will be transferred to the next trunk in a given preferential order. Since this order of preference for each of the twenty-five lines in a group is different, relays 40 I, 403 and 405 are provided for transferring the leads to the selecting magnets and relays 402, 404 and 406 are provided for transferring the holding magnet leads, as will hereinafter be explained. Relays SMI to SM-4 of Fig. 5 are provided for connecting the preference leads to selecting magnets associated with the particular group of twenty-five lines in which the call originates.

Thus far, the outline of a telephone exchange system embodying the features of this invention has involved a unit of one hundred lines as indicated in Fig. 7. It will, however, be evident that these features may readily be adapted to serve in telephone exchange systems where the unit is greater than one hundred lines and where a larger group of trunks is available. For example, Fig. 8 has been drawn to show the application of the features of this invention to exchange systems where units of two hundred lines and twenty trunks prove to be the most economical. In this figure, the four multiple appearances of one hundred subscriber lines are spread over four 100- point cross-bar switch banks 805 in such a manner that the lines occur in groups of different sizes the same as in Fig. '7, each such group appearing in a horizontal row of contacts in the switches and also in a vertical row of contacts in the switches. Moreover, there are two sets of these differentto battery.

sized groups, the lines which constitute the groups of one set differing from the lines which constitute the corresponding groups of the other set. For example, the group of nineteen lines occupying the bottom horizontal row of contacts in the drawings and also occupying the right-hand vertical row of contacts comprises lines to I8; whereas the group of nineteen lines occupying the upper horizontal and the left-hand vertical rows of contacts comprises lines 8I to 90. Likewise, the group of three lines occupying the middle part of the second horizontal row from the bottom of the two upper switches and also occupying the middle part of the ninth vertical row of the two left-hand switches comprises lines Nos. I, 2, and 3. An inspection will show that other pairs of corresponding groups are composed of different combinations of lines. Thus the different lines have access to a number of trunks through different groups, and each line has a preference for these trunks the same as in the arrangement of Fig. 7. A second set of four 100-point cross-bar switches 806, identical with the first set 805, provides for four appearances of each of the second group of one hundred lines. While no switching circuit connections are shown for the arrangement of Fig. 8, it will be readily understood that said electrical connections may be made on a basis similar to that shown in Figs. 1 to 6.

The invention having been described generally, a detail description of the operation of the apparatus shown will now be given. For this purpose it will be assumed that the subscriber at substation SI initiates the call. Upon removal of the receiver a bridge is placed across the line conductors IM and I02 of Fig. 1, which operates the relay L-I over a path traced from battery through winding of relay L-I, inner armature and break contact relay CO-I, line conductors lill and I02, including the subscribers bridge, then through outer contact and armature relay COI to ground. Operation of relay LI at its inner contact prepares a path for operating relay CI over conductors I and I I5, and at its outer contact closes a circuit for operating relay A--I of Fig. 2. The latter circuit may be traced from grounded battery, through winding of relay A--I top armature and contact of relay D-I, thence over lead H0 and outer contact relay L-I to lead I04, to ground through top inner contact and armature relay EI. Relay A--I operates and at its upper front contacts connects lead 506 to battery through lower winding relay BI. Lead 506, being a test lead running through the back contacts on other relays, A--I0 to A2, will be open at left back contact relay 503 if another call in the group of one hundred lines is in the process of selecting a trunk. Assuming, however, that relay 503 is unoperated, the ground from the top break contacts of relays 50I and 502 will be connected through break contact relays 503, lead 505, through armatures and break contacts on relays AI0 to A--2, make contact on operated relay A-I and through lower winding relay BI Relay B-I thus operates, but if simultaneous calls had originated on subscriber lines SI and S2 or SI and SIB, then relays 3-2 or BI0 respectively would have operated in the path previously traced in preference to relay B-I. Tracing further the call from line. SI, when relay BI operates, it closes a circuit from battery through its own top winding and front contact to another test lead 501 running through the armatures and break contacts on other B relays 75 to ground through winding of relay 503. The latter relay operating then opens lead 506 and remitting the lowest of the calling lines in any group of ten to search for a trunk and looking out all other lines until an idle trunk is found or until the call is timed out when another attempt is. made to select a trunk. 7

Before a search is made for an idle outgoing trunk for the call on line SI, it is necessary to find out in which vertical group of ten lines the calling line is. located, otherwise referred to as the horizontal preference. This is determined by the common relay 504 in upper right corner Fig- 5, and the relays CI to CI0, inclusive, together with lead 508. Therefore, immediately after the vertical preference is determined, described in the preceding paragraph, the B-I relay of Fig. 2

closes a circuit for operating relay CI of Fig. 4

over a path traced from ground at the top break contact relays 50I and 502 of Fig. 5, through armature and back contact relay 504, thence over multiple lead 509, contact 208 on relay BI,

multiple lead I I5, through operated inner contact on relay LI, multiple lead I05, top break contact and armature relay E-l, and through bottom winding relay CI to battery. Relay CI, in operatin locks to ground through its upper winding and front contact to lead 500, traced through all the top break contacts and armatures of relays CZ to CI0 thence through winding of relay 504 to ground at top contacts of relays 50I and 502. Relay 504, in operating, opens its own top contact which breaks the operating circuit previously traced for the lower winding of relay CI, thus preventing later calls that might originate in other groups of lines from interfering with the handling of the call on line SI. The identity or location of the calling line is thus established by virtue of the fact that only one of the B and one of the C relays; namely, B--I and CI remain operated. Before proceeding to show how this line is actually connected with an idle one of the outgoing trunks, it is thought that this vertical and horizontal preference will be more clearly understood if a description is given of several other cases where more than one line originates a call at the same time.

Assuming, for example, that subscribers on lines SI and S lift their receivers about the same time, line relay L-I and corresponding B-I and C.-I relays will operate as previously described. Line relay L--26 will also operate and connect ground that is on lead I I0 to lead I I 6. Since both relays L-I and L-26 connect ground to lead I I6, which path is further traced through relay AI, it is evident that only the B--I relay will operate. The vertical preference is thus determined by the topmost one in their respective subgroups. When, therefore, ground is placed on lead I I5 at contact 208 by relay B--I a circuit is established for operating both the CI and C0 relays, traced over lead II5 to right inner contact relay L25, lead I I I, top outer contact and armature relay E4 to battery through lower winding relay C4; also traced over lead II5 through inner contact relay LI,.lead I05, top outer contact and armature relay E--I, to battery through lower winding relay CI. In this case, the locking circuit through the upper Winding relay C4 is completed back over the series lead 508 to the winding of relay 504 to ground, while the locking circuit through the upper winding of relay CI is held BI relay being operated, both lines being theiefl open at Contact 401 on relay CI. Relay 504 operating, thus opens at its top break contact, the

circuit for energizing the lower windings of relays CI and C-4 so that relay CI releases and relay Clremains operated. In this manner, line S26 is identified as the calling line to be handled first, and search for an idle outgoing trunk will be directed by the combination of the BI and C4 relays remaining operated as will later be described.

Another example is assumed where subscriber lines SI, S25 and SI lift their receivers nearly simultaneously, in which case relay A-I operates over lead I I6 through contacts on relays LI and L26 as previously traced. Line relay LI 00 of Fig. 2, also operating, connects ground that is on lead 206 to lead 209, thence through top contact and armature on relay D-I0, through winding relay A-I0 to battery. The operation of relay AI0 causes relay BI0 to operate from ground "on lead 506, and at the same time the top break contact opens the circuit to the armature relay A--I and prevents relay BI from operating. The failure of relay BI to connect ground to lead H prevents relays CI and C4 from operating. On the other hand, relay-BI0 at contact 2I0 connects ground to lead 2I I for operating relay C8--L further'traced through inner contact relay LI00. lead 201, top break contact relay E--8L to battery through lower winding relay C8L. In this manner line I00 is identifiedas the calling line to be handled first and search for an idle outgoing trunk is determined by the combination of the BI0 and C8L relays remaining operated as will later be described. It should be observed at this point that each of the vertical rows, 3 and 8, of the L and CO relays are divided into two parts with the C and E relays corresponding to the upper set being designated 3U and 8-U, respectively, and for the lower set 3L and BL respectively. This makes it possible to arrange the four separate twenty-five line groups in two and one-half rows for each group.

Going back to the condition ensuing forthwith upon the identity of calling line SI being determined by relay BI of Fig. 2 and relay CI of Fig. 4 remaining in an operated condition, their will now be described the manner in which a search is made for an idle trunk. Relays 503 and 504 of Fig. 5, it will be remembered, are also in an operated condition at this time which prevents interference from other lines that might originate calls. Since each calling line has four possible chances for reaching an idle trunk, it will be assumed that the first choice trunk 305 is idle. Relay "I'K5 of Fig. 5, therefore, is normal because if the trunk 305 Were busy it would be operated as it will presently appear.

Relay 503 in addition to opening the circuit of test lead 506 also connects ground from the top break contacts of relays SM and 502 to multiple lead 5I0, thence through contact 2II on relay BI, and through upper winding relay D-I to lead 2I2, through inner make contact relay740l, which is operated at this time, lead-408, armature 5I I, and back contact on relay TK5 thence over leads 5I2 and 5I3 to armature 5I4 and front contact on operated relay SMI, thence overlead5 I 5, and through resistance 3I5 of Fig. 3 to. battery through winding of selecting magnet 3I6. In the path just traced, relayI of Fig. 4 is operated because relay CI'connects ground at contact 1409 to multiple lead 4 I 0, thence to battery through for slow release relay AI.

winding relay MI. in like manner, relay SlVi-I of Fig.5 is operated because relay CI connects ground at contact 4| I to multiple lead H2, thence to battery through winding relay SM-I. Having operated the selecting magnet 3I6 in cross-bar switch LB-I of Fig. 3 corresponding to the horizontal row in which the multiple of line SI first appears, contact 3H on the magnet short-circuits resistance 3I5 thereby causing the marginal relay D-I of Fig. 2 to operate and open the circuit The latter relay delays releasing long enough to hold ground on the circuit for operating relay 505 of Fig. 5 over a path traced through its own armature 2 I 3, armature 2M and front contact relay DI, lead 2I5, through winding relay 505 to battery.

When marginal relay D-I operated, it established a locking circuit for itself at contact 2| 6 to multiple lead 2 I 'I which prevents locking out calls in the upper half of the vertical rows of L and CO relays due to an abnormal number of calls continuin'g to originatein the lower half of the rows.

Thus, if another call is waiting in the first group, for example, when relay D-I 0 operates on a call,

the latter relay remains operated due to lead 2I1 being grounded by contact 2 I8 on relay A-I In this manner, during the busy hour, each D relay will remain operated until all-D relays have operated or until no more calls are Waiting.

'Rela'y 505 operating, locks to ground on contacts of relays 5M and 502 and at its bottom make contact closes a circuit from'ground for operating the cross-bar switch holding magnets and for operating relay Bill and in turn relay 502. The latter two relays are slow releasing and slow operating, respectively, timed so that the holding magnet will be assured of suificient time to fully operate, after which relay 505 will be released and the operating path to the holding magnets broken. The circuit previously mentioned for operating the holding magnet corresponding to first choice trunk 305 for calling subscriber SI,

may be traced from ground on lower armature and make contact relay 505 to lower armature and front contact relay 506, lead 5I6, thence through contact M3 on operated CI relay, lead M4 to battery through winding relay 402. The latter relay operates and prepares the ten leads indicated at M5 for operating one of the holding magnets determined by which one of the BI to BIO relays of Fig. 2 is in an operated position and whether any of the TK relays are operated. The circuit for the holding magnet in case of line I, is determined by relay BI and may be traced from ground on the contacts of relays 50I and 502 through operated make contact relay 503, multiple lead 5I0, contact 2I9 on relay BI to lead 220, armature and contact M6 of relay 402, lead 4|! to armature 5" on TK-5 relay of Fig. 5, thence over back contact to lead SH! and battery through right-hand winding holding magnet H--5 of switch LB-4 of Fig. 6. The latter operates in this circuit and at contact 60I establishes a holding path for itself as will later be explained and at contact 602 prepares a path to lead 5I9 for operating relay TK-5 and at its left inner contact connects ground for operating the corresponding holding magnets on the other three cross-bar switches, namely, LB-3, LB2 and LBI connected in series. Inasmuch as the 'only'selecting magnet operated at this time is 3 I 6 of Fig. 3, the contact points at cross-point for line I will be the only one closed, thus connecting line I'directly'with trunk 305 traced over lead I03,

-lead 3II,'-line I contacts of cross-bar switch LBI, trunk 305 to an incoming selector at T. not shown.

In the system of this invention, upon connecting with an idle trunk, ground is returned over the sleeve or control wire thus traced for holding the connecting switches until the subscriber restores his receiver to the switch-hook, all in a manner well understood in the art. Therefore,

upon the closure of contact I in the switch LB-I, ground may be traced on the sleeve of trunk 305, back over leads 3 and I03 to battery through COI relay of Fig. 1, thus causing line relay LI to release. Ground returned on the sleeve of trunk 305 may also be traced through contact GM and left winding on holding magnet H5 to the mid-point of the magnet windings to which direct operating ground was traced in the previous paragraph. Thus, when the timing relays 50I and 502 of Fig. 5 previously referred to operate and remove ground from the lead connected to the midpoint of holding magnet H-5, the magnet continues to remain operated on the trunk holding ground through both windings in series. Furthermore, when relay 505 releases due to the operation of relays 50I and 502, ground will be connected to multiple lead 524 for operating relay 'I'K--5 over a path traced through contact 602 on magnet H-5, lead 519 and battery through upper winding relay TK5. The latter relay operates, thereby transferring the trunk selecting circuit to the next choice trunk. Relay TK-5 closes a locking circuit for itself back over lead 525 to the sleeve of trunk 305 and thereby remains operated as long as the connection is held by the subscriber. Relay 505, being released, permits relays 50I and 502 to release after a short interval and restore the circuits to normal for the next call.

Having described a call from subscriber line SI on the assumption that the outgoing trunk 305 was idle, this call will now be described on the assumption that trunk 305 is busy and that the next trunk choice is available. In this case it will be observed that the second choice appearance of line SI is in switch LB--I at the lower left corner of Fig. 3 wires to connect with trunk 30I which, for this case, is assumed to be idle. Thus, all cross-bar switch contacts associated with this trunk are open and relay 'I'KI of Fig. 4 and holding magnets are unoperated. It will be remembered that removal of the subscribers receiver from the switch-hook caused the BI relay of Fig. 2 and the C--I relay of Fig. 4 to operate and mark the location of the calling line. These relays, together with relays 503 and 504 of Fig. 5, remain operated until the line is connected to a trunk. Thus, when relay 503 of Fig. 5 first operates and connects ground to a circuit, including lead 5I0 and top winding relay D--I of Fig. 2 and leads 2| 2 and 408 as previously described, said ground path is further traced through armature 5 on relay TK--5 which is now operated due to trunk 305 being busy. The path just traced at the front contact 520 relay TK5 thus may further be traced over lead 52 I,

armature 4I0, and back contact on relay TK--I, thence over multiple lead 4 I 9, through contact 522 on relay SMI lead 523, to battery through resistance 3H3 and selecting magnet 3I0 of crossbar switch LBI.

The selecting magnet 3I9 operating, short-circuits at its bottom contact resistance 3H0 thus increasing the flow of current through selecting magnet circuit which includes marginal relay D-I. The latter relay operates, causing relay 505 to operate over lead 2I5 previously traced. Relay 505 operating, closes a circuit for relay 402 over a path traced from ground on its bottom armature and. front contact, bottom armature and front contact relay 504, lead 5H5, contact M3 on relay C-I, lead M4 to battery through relay 402. Relay 402 operating, prepares the ten leads indicated at M 5 for operating one of the holding magnets as previously described. The holding magnet HI of switch LB4 in this case, therefore, is operated by ground through contact 2I9, relay B-I to armature 5II, relay TK5 previously traced and further traced over front contact relay TK-5, lead 520, armature 420 and back contact relay TK-I, lead 42I, to mid-point on holding magnet H-I of the switch LB4. Line I is thus connected to trunk 30I at contact I on switch LBI due to ground at inner contact on magnet I-I--I of switch LB4, being connected to the HI holding magnets of the other switches LB-3, LB-2 and LB-I in series. In the same manner as previously described for trunk 305, ground returned over the sleeve of trunk 30I is connected through contact 003 of holding magnet H-I of switch LB-4 for maintaining the latter operated during the time it is busy. The magnet H-I likewise closes a contact 604 for operating busy relay TK-I over leads 524 and 60! upon the release of relay 505 of Fig. 5 which occurs when the selecting circuits are ready for the next call. Relay TK--I operated, locks over lead 608 to the sleeve of trunk 30I.

It will be evident from the above description of the call on line Si selecting first trunk 305 and then trunk 30I, that the busy relays TK5 and TK-I determine which selecting and holding magnets are to be energized in accordance with the trunk choices which each line has. To illustrate further, in the case of line SI, if trunks 305 and 30I are busy and trunk 3I0 is idle, then relays TK5 and TK--I will be operated and relay TK-I normal when line SI originates the call. The selecting magnet path in this case at armature 4 I0 on relay TK-I may further be traced over the front contact, lead 440, armature 521 and back contact relay TKI 0, leads 520 and 4 I9, through contact 522 on relay SM-I, lead 523 to the battery through resistance 3I8 and selecting magnet 3I0. The holding magnet path at armature 420 on relay TKI may further be traced over the front contact, lead 422, armature 529 and back contact relay TKI0, lead 530 to battery through midpoint and right-hand winding on holding magnet HI0 of switch LB-4. Line SI in Fig. 1 is therefore connected over leads I03 and 3I3 to trunk 3I0 at contact I in the lower right-hand corner of cross-bar switch LB-I shown in Fig. 3.

Considering now the case where trunks 305, 30I and 3I0 are busy, line SI will be connected with trunk 300. The selecting magnet path in this case at armature 521 on relay TK--I0 may further be traced over the front contact, lead 530, armature 53I and back contact relay TK-5, leads 532 and I3, through contact 5I4 on relay SM-I, lead5I5 to battery, through resistance 3 I 5 and selecting magnet 3 I 0. The holding magnet path at armature 520 on relay TK--I0 may also further be traced over the front contact, lead 533, armature 534 and back contact relay TK0, lead 535 to battery through mid-point and right winding on holding magnet H0 of switch LB4. Line SI of Fig. l in this manner is connected over leads I03 and BM to trunk .306 at contact I on the switch LB-l.

It may happen that all four trunks to which line SI has access are busy. In this event, the selecting magnet path at armature 53I on relay 'I'K6 may further be traced over the front contact, lead 536 to multiple lead 523, in Fig. 4, thence through contact 424 on relay C-I, resistance 425, to battery through relay EI. The latter relay is slow releasing and functions in the place of what would have been the selecting magnet of the next choice trunk by closing a short circuit around resistance 425, thus permitting marginal relay DI to operate and energize the holding magnet path, thereby permitting relays 50I and 502 to function by timing out the call, the holding magnet path at this time being held open. Relay EI operating, also opens the circuit at its top contacts over leads I04 and I05, preventing other calls in the vertical row of L and CO relays from getting a trunk assignment until after the slow release EI relay releases. This release period is relatively short but it is sufficient to prevent calls whose trunk choices are all busy, from delaying those calls where trunks are available. Said E--I relay may also be used for registering an all-trunks busy condition or for giving an alarm if desired.

Referring nowto that assumption in a previous paragraph of the two lines SI and S26 calling simultaneously, it was shown that line S26 would first receive a trunk assignment. It will further be observed that line S26 which is the first line in the second group of twenty-five lines, appears in the bank of cross-bar switch LB2 in the same relative multiple positions as line I did in the bank of switch LBI. Thus, identically the same circuit paths are employed for assigning'the same trunks in the same order as for-line I. However, in place of operating the selecting magnets of cross-bar switch LBI, the selecting magnets of switch LB--2 are energized due to the SM--2 relay of Fig. 5 being operated in place of relay SM-I. This is brought about due to relay C4 being operated instead of C-I, so that ground at contact 426 on relay C4 is connected to lead 421 and thence through winding of relay SM'2 to battery. Line S26 is, therefore, connected over lead II1 to the first idle one of the trunks 305, Mi, 3l0 or 306, the same as line SI would be. Likewise, lines S5I and S16 being the first line in their respective third and fourth groups have the same trunk assignment as'for lines SI and S26.

When three lines, such as SI, S26 and SI00, originate calls simultaneously, as previously discussed, it was shown that line SI would receive a trunk assignment first. It will further be observed that compared with line SI, line SI00 not only has its multiple appearances in a different cross-bar switch LB--4, but that the position of its multiple appearancesis also different, such that'the. line may have access to trunks'30I,.305,.306 and 302 in the order shown.

The switching of the selecting and holding magnet leads to accomplish this, as before stated, is dependent on relays B-I 0 and C--8--L. Tracing further the call on line SI 00 under the above conditions and under the further assumption that only trunk 302 is idle, it will first be noted that all selecting magnet leads indicated at 538 are connected to the magnets of switch LB4 due to relay SM4 being operated over lead 531 by relay C--8-L at contact'539. The latter relay at contact 540 also connects ground to lead 54I for operating relay 405, the function of which is-to prepare the pathsto the selecting magnets for control by the B and D relays. When, therefore, relay 503 of Fig. 5 operates, ground at back contact relays 50I and 502 is connected to lead 5I0, traced further through contact 22I on relay BI0, upper winding relay D-I0, thence over leads 222 and 428, contact 429 on relay 405, armature 430 on TKI relay and front contact to lead 43I, armature 54I on TK-5 relay and front contact to armature 542 on TK6 relay and front contact to lead 543, armature 432 on relay TK2 and back contact to lead 433 through contact 544 on SM4 relay, lead 545 to battery through resistance 605 and selecting magnet 606 of cross-bar switch LB4. The operation of the selecting magnet in the path just traced, short-circuits the resistance 605 causing marginal relay D-I0 to operate and close a ground path for operating the holding magnet H2 of switch LB4. Relay D-I0 first operates relay 505 over lead 2I5 which looks to ground on contacts of timing relays 50I and 502. Relay 505 at its bottom make contact connects ground to lead 5I6 for operating timing relays 50I and 502 as previously described. Ground on lead 5I6 also operates relay 406 of Fig. 4 over a path traced through contact 546 on relay C8L, thence over lead 541 to battery through relay 406. The latter relay prepares the holding magnet circuit and together with the BI 0 relay causes holding magnet H2 to operate. This path is traced from ground on contacts of relays 50I and 502, operated contact relay 503, lead 5I0, contact 223 on relay BI0, leads 224 and 434, contact 435 on relay 406, armature 436'on relay TK--I, and front contact to lead 438, armature 541 on relay PK-5 and front contact, armature 548 on relay TK-6 and front contact to lead 549, armature 431 and back contact to lead 439, to the mid-point of windings on holding magnet H2 and battery through its right-hand winding. Line SI00 of Fig. 2 will thus be connected over lead II8 to trunk 302 at contact I in the upper left corner of cross-bar switch LB4 shown in Fig. 6.

It will further be understood from the foregoing description that a multiple arrangement of subscriber lines is provided which gives every subscriber line four equal chances for being connected to an incoming selector or district junctor circuit and'at the same time, for maintenance reasons, allows for the numbering of the multiple appearances in each switch in a simple uniform manner.

What is claimed is:

1. The combination in a switch comprising coordinate rows of separately operable switch contacts of lines arranged in groups of different sizes, said groups appearing in respective horizontal rows of said contacts and also in respective vertical rows of said contacts, and means for selectively operating said contacts.

2. The combination in a switch having horizontal and vertical rows of separately operable switch contact sets, all of said rows having the same number of contact sets therein, of a number of groups of lines appearing respectively in horizontal rows and respectively in vertical rows of said switch, each of said groups occupying a difi'erent number of contact sets in the row to which it is assigned, and cross-bar means for operating said contact sets.

3. The combination in a switch comprising vertical and horizontal rows of separately operable contact sets of a group of lines comprising a particular line in combination with certain other lines appearing in a vertical row and also in a horizontal row of said contact sets, and a second group of lines comprising said particular line and a different combination of other lines appearing in a vertical row and also in a horizontal row of said contact sets.

4. In combination, a plurality of cross-bar switches, vertical and horizontal rows of contact sets in said switches, and a plurality of groups of lines, each group appearing in a horizontal row in a number of said switches and also in a vertical row in a number of said switches.

5. In combination, a plurality of cross-bar switches, vertical and horizontal rows of contact sets in said switches, and a plurality of line groups of different sizes, each group appearing in vertical rows of contacts in some of said switches and in horizontal rows in other of said switches.

6. In combination, an automatic switch having a plurality of separately operable contact sets arranged in vertical rows and horizontal rows, lines arranged in groups of different sizes, each line group appearing in a vertical row and also in a horizontal row of contacts, said lines appearing individually in a plurality of said groups, and means for operating said contacts.

7. In combination, an automatic switch having a plurality of separately operable contact sets arranged in vertical rows and in horizontal rows,

subscribers lines arranged in groups of difierent sizes, each line group appearing in a vertical row of contacts and multipled to appear in a horizontal row of contacts, each line appearing individually in a plurality of said groups, connecting circuits appearing in said contact sets, and means for operating said contact sets to connect a particular line to one of said connecting circuits either through a set of contacts in a vertical row or through a set of contacts in a horizontal row.

8. The combination in a switch for extending subscribers lines in telephone connections comprising coordinate rows of separately operable switch contacts, subscribers lines arranged in groups of different sizes, said groups appearing in respective horizontal rows of said contacts and also in respective vertical rows of said contacts, and means for selectively operating said contacts.

9. The combination in a switch for extending subscribers lines in telephone connections comprising coordinate rows of separately operable switch contacts, subscribers lines arranged in groups of different sizes, the lines of said groups being connected to the contacts in respective horizontal rows of said contacts and also connected to the contacts in respective vertical rows of said contacts, and means for selectively operating said contacts.

THOMAS A. SPENCER. 

